The present invention relates to an image processing circuit performing a gradation conversion of image data (a gradation data set), a gradation converting method, and a printing apparatus performing a gradation conversion of image data at the time of printing images of the image data.
In general printers currently available on the market, an image processing circuit generates data for operating a print engine on the basis of an RGB data set which a CPU in the printer generates by analyzing print data (or, on the basis of an RGB data set which is transmitted, as print data, from a host). However, existing image processing circuits are configured to decrease the number of gradations.
Specifically, as an image processing circuit for a color printer, there is an image processing circuit having a configuration shown in FIG. 6. In the image processing circuit, a gradation converting circuit 52 converts 8-bit Z data sent (Z=C, M, Y, and K) from a color converting circuit 51 into 8-bit Z′ data by the use of a gradation conversion table as shown in FIG. 7 (gradation conversion table for performing a gradation conversion as shown in FIG. 8). The color converting circuit 51 is a circuit for converting 8-bit R, G, and B data into 8-bit C, M, Y, and K data. A binarization and smoothing processing circuit 53 is a circuit for converting the Z′ data supplied from the gradation converting circuit 52 into Z″ data (data for operating the print engine) to be used as a depiction width of each pixel.
Since it is necessary to perform the gradation conversion shown in FIG. 8, some values are not set as outputs in the gradation conversion table. Accordingly, in the image processing circuit, the number of gradations is reduced by the processing of the gradation converting circuit 52.
In another image processing circuit different from the circuit shown in FIG. 6 in a specific configuration, the gradation converting process of decreasing the number of gradations is performed in a manner similar to the case of the above-mentioned image processing circuit (e.g., see Japanese Patent Publication No. 2006-197359A).